Polishing apparatus and polishing method

ABSTRACT

A polishing apparatus for polishing a workpiece includes a chuck table having a holding surface for holding the workpiece placed on the holding surface under suction thereon, a polishing unit for polishing the workpiece held on the chuck table with a polishing pad while supplying a slurry to the workpiece, and a high-pressure steam ejecting unit having a nozzle for ejecting high-pressure steam to the holding surface of the chuck table. The high-pressure steam ejecting unit ejects high-pressure steam to swarf produced from polishing the workpiece and deposited on an outer circumferential portion of the holding surface for thereby removing the swarf from the holding surface.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer and a polishing method for polishing such a workpiece with a polishing apparatus.

Description of the Related Art

According to a fabrication step for fabricating device chips to be used in electronic equipment such as mobile phones and computers, a plurality of devices such as integrated circuits (ICs) or large-scale-integration (LSI) circuits are initially formed on a face side of a semiconductor wafer. Next, a reverse side of the semiconductor wafer is ground to thin the semiconductor wafer to a predetermined thickness, and then the semiconductor wafer is divided into individual device chips. When the reverse side of the semiconductor wafer is ground, minute surface irregularities are formed as grinding marks on the ground reverse side. Such minute surface irregularities remain as they are on the device chips divided from the semiconductor wafer. The minute surface irregularities are responsible for a reduction in the flexural strength of the device chips. It is known in the art to polish the reverse side of the wafer according to a chemical mechanical polishing (CMP) process or the like after the wafer has been ground (see JP Hei 8-99265A).

A polishing apparatus for polishing a workpiece such as a wafer includes a chuck table for holding the workpiece on a holding surface thereof and a polishing unit having a polishing pad mounted thereon for polishing the workpiece held on the chuck table. When the workpiece is polished by the polishing apparatus, minute surface irregularities on the ground surface of the wafer are removed, giving the wafer a mirror finish. While the workpiece is being polished on the polishing apparatus, the surface being polished of the wafer is supplied with a slurry as a polishing fluid. The slurry is a chemical fluid with abrasive grains dispersed therein, for example. The slurry contributes not only to the polishing of the wafer through chemical and mechanical actions, but also to the discharging of swarf produced from polishing the wafer. The slurry is supplied from a supply channel defined centrally in the polishing pad, and travels between the polishing pad and the workpiece to an outer circumferential edge of the workpiece.

SUMMARY OF THE INVENTION

After having reached the outer circumferential edge of the workpiece, the slurry that contains the swarf falls off the surface being polished of the wafer and is deposited on and adheres to an outer circumferential portion of the holding surface of the chuck table. When the polished workpiece is unloaded from the chuck table, therefore, the adhering swarf remains on the holding surface of the chuck table in surrounding relation to an area of the holding surface where the workpiece has been present.

When a workpiece to be polished by the polishing pad is to be loaded onto the chuck table, the adhering swarf on the chuck table tends to enter between the chuck table and the workpiece, obstructing the loading of the workpiece onto the chuck table. One solution is to supply cleaning water to the outer circumferential portion of the holding surface of the chuck table in order to remove the adhering swarf from the chuck table. However, it is not easy to remove the adhering swarf from the chuck table with the cleaning water. According to another solution, a sufficient amount of cleaning water is supplied to the outer circumferential portion of the holding surface of the chuck table while the workpiece is being polished by the polishing pad in order to wash away the slurry before the slurry containing the swarf that has reached the outer circumferential portion of the holding surface adheres to the holding surface. However, one problem with the latter solution is that the supplied cleaning water is mixed with the slurry supplied between the polishing pad and the workpiece, thinning down the slurry to the extent that the polishing process cannot be performed properly.

It is therefore an object of the present invention to provide a polishing apparatus and a polishing method that are capable of removing swarf produced from polishing a workpiece held on a chuck table and adhering to an outer circumferential portion of the chuck table.

In accordance with an aspect of the present invention, there is provided a polishing apparatus for polishing a workpiece, including a chuck table having a holding surface for holding the workpiece placed on the holding surface under suction thereon, a polishing unit for polishing the workpiece held on the chuck table with a polishing pad while supplying a slurry to the workpiece, and a high-pressure steam ejecting unit having a nozzle for ejecting high-pressure steam to the holding surface of the chuck table. The high-pressure steam ejecting unit ejects high-pressure steam to swarf produced from polishing the workpiece and deposited on an outer circumferential portion of the holding surface for thereby removing the swarf from the holding surface.

In accordance with another aspect of the present invention, there is provided a polishing method to be carried out by a polishing apparatus including a chuck table for holding a workpiece placed on a holding surface under suction and a polishing unit for polishing the workpiece held on the chuck table with a polishing pad while supplying a slurry to the workpiece, the polishing method including a holding step of placing the workpiece on the holding surface and holding the workpiece on the chuck table, a polishing step of polishing the workpiece held on the chuck table with the polishing pad while supplying the slurry to the workpiece, an unloading step of unloading the workpiece polished in the polishing step from the chuck table, and a swarf removing step of ejecting high-pressure steam to swarf produced from polishing the workpiece and deposited on an outer circumferential portion of the holding surface for thereby removing the swarf from the holding surface.

With the polishing apparatus and the polishing method according to the above aspects of the present invention, the workpiece is polished by the polishing pad while the slurry is being supplied to the workpiece. When the workpiece is ground, swarf produced from polishing the workpiece is deposited on the outer circumferential portion of the holding surface of the chuck table. The high-pressure steam is ejected to the swarf adhering to the outer circumferential portion of the holding surface, softening the swarf because the swarf is heated and water is applied to the swarf. Therefore, when the high-pressure steam is continuously ejected to the swarf, the adhering swarf can be removed relatively and easily from the holding surface. Upon removal of the swarf from the holding surface, a new workpiece can be placed on the holding surface without fail.

According to the above aspects of the present invention, consequently, there are provided a polishing apparatus and a polishing method that are capable of removing swarf adhering to the outer circumferential portion of the chuck table.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically illustrating a polishing apparatus according to an embodiment of the present invention;

FIG. 2 is a perspective view schematically illustrating a polishing wheel of the polishing apparatus;

FIG. 3 is a perspective view schematically illustrating a manner in which a protective member is affixed to a face side of a workpiece to be polished;

FIG. 4 is a perspective view schematically illustrating a manner in which the workpiece is placed on a holding surface of a chuck table of the polishing apparatus;

FIG. 5 is a perspective view schematically illustrating a manner in which the workpiece is polished by the polishing wheel;

FIG. 6 is a perspective view schematically illustrating a manner in which the workpiece that has been polished is unloaded from the holding surface of the chuck table;

FIG. 7A is a perspective view schematically illustrating a manner in which an outer circumferential portion of the holding surface of the chuck table is cleaned;

FIG. 7B is a perspective view schematically illustrating the chuck table after the holding surface thereof has been cleaned;

FIG. 8A is a flowchart of a sequence of steps of an example of a polishing method for polishing a workpiece;

FIG. 8B is a flowchart of a sequence of steps of another example of the polishing method; and

FIG. 8C is a flowchart of a sequence of steps of still another example of the polishing method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. First, a workpiece to be polished by a polishing apparatus and a polishing method according to the preferred embodiment will be described below with reference to FIG. 3. FIG. 3 schematically illustrates in perspective a workpiece 1 such as a semiconductor wafer. The workpiece 1 may include, for example, a wafer made of silicon, silicon carbide (SiC), or other materials including a semiconductor or the like, or a substrate shaped as a substantially circular plate made of sapphire, glass, quartz, or the like. The workpiece 1 has a face side 1 a where a plurality of areas are demarcated by a grid of projected dicing lines or streets 5 established on the face side 1 a. A plurality of devices 7 such as ICs or LSI circuits are formed respectively in the areas on the face side 1 a. The workpiece 1 will be divided finally along the projected dicing lines 5 into individual device chips including the respective devices 7.

The workpiece 1 is thinned down by having a reverse side 1 b thereof ground. The ground reverse side 1 b of the workpiece 1 has minute surface irregularities formed as grinding marks. If the workpiece 1 with the minute surface irregularities left on the reverse side 1 b is divided along the projected dicing lines 5 into individual device chips, then the minute surface irregularities remain as they are on the device chips and are responsible for a reduction in the flexural strength of the device chips. To alleviate such a drawback, the ground reverse side 1 b of the workpiece 1 is polished to remove the minute surface irregularities therefrom, making the reverse side 1 b flat. Therefore, no minute surface irregularities remain on the device chips divided from the workpiece 1.

In preparation for the process of polishing the reverse side 1 b of the workpiece 1, a protective tape 3 is affixed in advance to the face side 1 a of the workpiece 1 to protect the face side 1 a. The protective tape 3 protects the face side 1 a of the workpiece 1 from shocks to be caused by polishing the reverse side 1 b of the workpiece 1 is polished, delivering the workpiece 1, and otherwise handling or processing the workpiece 1. The protective tape 3 has a flexible film-shaped base and a glue layer, i.e., an adhesive layer, formed on a surface of the base. The base is made of polyolefin, polyethylene terephthalate, polyvinyl chloride, polystyrene, or the like, for example. The glue layer is made of silicone rubber, an acrylic material, an epoxy material, or the like, for example.

A polishing apparatus according to the present embodiment for polishing the reverse side 1 b of the workpiece 1 as a surface to be polished will be described below. FIG. 1 illustrates a polishing apparatus, denoted by 2, in perspective. As illustrated in FIG. 1, the polishing apparatus 2 has a base block 4 supporting various components thereof. The polishing apparatus 2 includes two cassette rests 6 a and 6 b on an upper surface of a front portion of the base block 4. A cassette 8 a storing therein a plurality of workpieces 1 to be polished is placed on the cassette rest 6 a, for example. A cassette 8 b storing therein a plurality of workpieces 1 that have been polished is placed on the cassette rest 6 b, for example. A workpiece deliver robot 10 for delivering a workpiece 1 at a time is installed on the base block 4 adjacent to the cassette rests 6 a and 6 b.

On the upper surface of the front portion of the base block 4, there are also disposed a positioning table 12 for adjusting the position of a workpiece 1 by gripping the workpiece 1 with a plurality of positioning pins and a workpiece loading mechanism or arm 14 for placing a workpiece 1 on a chuck table 20. In addition, a workpiece unloading mechanism or arm 16 for taking a polished workpiece 1 from the chuck table 20 and a spinner cleaning device 52 for cleaning and spin-drying a polished workpiece 1 are disposed on the upper surface of the front portion of the base block 4.

The base block 4 has an opening 4 a defined in an upper surface of a rear portion thereof. The opening 4 a houses therein an X-axis movable table 18 with the chuck table 20 placed on an upper surface thereof for holding a workpiece 1 under suction thereon. The X-axis movable table 18 is movable in X-axis directions, i.e., horizontal directions, by an X-axis moving mechanism, not illustrated. The X-axis movable table 18 is selectively positioned in a loading/unloading area 22 where a workpiece 1 can be placed on and removed from the chuck table 20 and a processing area 24 where a workpiece 1 held under suction on the chuck table 20 is polished. The chuck table 20 includes a porous member shaped as a circular plate having a diameter that is essentially the same as the diameter of the workpiece 1. The porous member has an upper surface exposed upwardly and defining an upper surface of the chuck table 20 as a holding surface 20 a for holding the workpiece 1 thereon. The chuck table 20 has a suction channel, not illustrated, defined therein that has an end held in fluid communication with the porous member and another end connected to a suction source, not illustrated. When the suction source is actuated, it generates a negative pressure that is transmitted through the suction channel and the porous member to the workpiece 1 placed on the holding surface 20 a, holding the workpiece 1 under suction on the holding surface 20 a. The chuck table 20 is rotatable about an axis perpendicular to the holding surface 20 a.

A polishing unit 26 for polishing a workpiece 1 is disposed above the processing area 24. The polishing unit 26 is supported on a support wall 28 erected on a rear end of the base block 4 of the polishing apparatus 2. Specifically, a pair of Z-axis guide rails 30 extending in Z-axis directions, i.e., vertical directions, are mounted on a front vertical surface of the support wall 28. A Z-axis movable plate 32 is vertically slidably mounted on the Z-axis guide rails 30. A nut, not illustrated, is disposed on a reverse side, i.e., rear surface, of the Z-axis movable plate 32 and operatively threaded over a Z-axis ball screw 34 extending between and parallel to the Z-axis guide rails 30. The Z-axis ball screw 34 has an end coupled to a Z-axis stepping motor 36. When the Z-axis stepping motor 36 is energized, it rotates the Z-axis ball screw 34 about its central axis, causing the nut to move the Z-axis movable plate 32 in the Z-axis directions along the Z-axis ball screw 34. The polishing unit 26 is fixedly mounted on a lower portion of a face side, i.e., front surface, of the Z-axis movable plate 32. Therefore, when the Z-axis movable plate 32 is moved in the Z-axis directions, the polishing unit 26 is also moved in the Z-axis directions in unison therewith.

The polishing unit 26 includes a spindle 40 movable about its central axis extending vertically by an electric motor coupled to a proximal end of the spindle 40 and a polishing wheel 44 fixed by fasteners 46 to a wheel mount 42 disposed on a distal end of the spindle 40. The electric motor is housed in a spindle housing 38 in which the spindle 40 is rotatably supported. When the electric motor is energized, it rotates the spindle 40 about its central axis, causing the polishing wheel 44 to rotate in unison with the spindle 40.

FIG. 2 schematically illustrates a polishing surface side of the polishing wheel 44 in perspective. The polishing wheel 44 includes a polishing pad 44 b made of felt of urethane or the like and having a diameter larger than the diameter of the reverse side 1 b of the workpiece 1 and a wheel base 44 a having a surface to which the polishing pad 44 b is fixedly attached. The wheel base 44 a has a plurality of fastener holes, not illustrated, defined in a surface thereof that is opposite the surface to which the polishing pad 44 b is fixedly attached. The fasteners 46 are threaded through the wheel mount 42 into the respective fastener holes, fastening the polishing wheel 44 to the wheel mount 42. The wheel base 44 a and the polishing pad 44 b of the polishing wheel 44 have a through hole defined therein that extends centrally thicknesswise therethrough. The through hole has an end in the polishing pad 44 b that acts as a polishing fluid supply port 54.

As indicated by the broken lines in FIG. 1, the polishing unit 26 has a polishing fluid supply passage 50 defined therein that extends vertically in the Z-axis directions. The polishing fluid supply passage 50 has an upper end connected to a polishing fluid supply source 48 and a lower end connected to the polishing fluid supply port 54. When the workpiece 1 is polished by the polishing unit 26, a polishing fluid referred to as a slurry is supplied from the polishing fluid supply source 48 through the polishing fluid supply passage 50 to the polishing fluid supply port 54 (see FIG. 2) defined centrally in the polishing pad 44 b. The slurry is a chemical fluid with abrasive grains dispersed therein, and the material of the abrasive grains, the diameter of the abrasive grains, the kind of a dispersion medium used, etc., are appropriately selected depending on the material of the workpiece 1. The abrasive grains may be made of, for example, silica, alumina, zirconia, manganese dioxide, ceria, colloidal silica, fumed silica, boehmite, bayerite, diamond, or the like. The dispersion medium may be made of, for example, an alkali aqueous solution of potassium acetate, potassium chloride, potassium hydroxide, sodium hydroxide, ammonium carbonate, potassium hydrogencarbonate, sodium hydrogencarbonate, imidazole, pyrazole, pyrazine, or the like. However, the materials that are contained in the slurry are not limited to the above materials, and other additives, etc., may be added to the slurry.

For polishing a workpiece 1 held on the chuck table 20 positioned in the processing area 24, the polishing pad 44 b is positioned above the workpiece 1 on the chuck table 20. Then, the polishing wheel 44 and the chuck table 20 are rotated about their respective axes extending vertically in the Z-axis directions, and the polishing wheel 44 is lowered to bring the polishing pad 44 b into contact with the workpiece 1. At this time, the polishing fluid supply source 48 is actuated to send the slurry to the polishing fluid supply passage 50, thereby supplying the slurry between the workpiece 1 and the polishing pad 44 b.

FIG. 5 schematically illustrates in perspective the manner in which the workpiece 1 is polished by the polishing unit 26. For polishing the workpiece 1, the chuck table 20 is rotated at a speed of approximately 300 rpm, and the polishing wheel 44 is rotated at a speed of approximately 1000 rpm, for example. The chuck table 20 is positionally adjusted in advance such that the polishing fluid supply port 54 in the polishing pad 44 b is closed by the workpiece 1. Therefore, the slurry supplied from the polishing fluid supply port 54 stays on the workpiece 1. When the polishing pad 44 b and the workpiece 1 are rotated about their respective axes extending vertically in the Z-axis directions while they are being held against each other, the slurry enters between the polishing pad 44 b and the surface to be polished, i.e., the reverse side 1 b, of the workpiece 1.

As the workpiece 1 is polished by the polishing pad 44 b, the surface being polished, i.e., the reverse side 1 b, of the workpiece 1 produces swarf. The swarf is entrained in the slurry and discharged toward the outside of the polishing pad 44 b. A slurry, denoted by 56 in FIG. 5, that has entrained the swarf reaches an outer circumferential portion of the reverse side 1 b of the workpiece 1, and drops off onto an outer circumferential portion 20 b of the holding surface 20 a of the chuck table 20. Thereafter, a part of the slurry 56 drops off the chuck table 20 and is discharged from a drain port 4 b (see FIG. 1) defined in the bottom of the opening 4 a in the base block 4 of the polishing apparatus 2. On the other hand, another part of the slurry 56 that has dropped off onto the outer circumferential portion 20 b of the holding surface 20 a of the chuck table 20 dries on the outer circumferential portion 20 b and adheres together with the swarf to the outer circumferential portion 20 b. On the reverse side 1 b of the workpiece 1, the temperature of the slurry is kept relatively high due to the heat generated by the polishing of the reverse side 1 b. However, since the temperature of the slurry that has dropped off onto the outer circumferential portion 20 b of the holding surface 20 a falls quickly, the slurry tends to adhere soon to the outer circumferential portion 20 b. FIG. 6 schematically illustrates in perspective the manner in which the workpiece 1 that has been polished is unloaded from the holding surface 20 a of the chuck table 20. As illustrated in FIG. 6, an adhering swarf, denoted by 9, remains on the outer circumferential portion 20 b of the holding surface 20 a of the chuck table 20.

While the polishing apparatus 2 is in operation, a plurality of workpieces 1 stored in the cassette 8 a are taken one after another from the cassette 8 a, loaded on the chuck table 20, polished by the polishing unit 26, unloaded from the chuck table 20, cleaned and spin-dried by the spinner cleaning device 52, and stored in the cassette 8 b. The workpieces 1 to be polished are placed successively on the holding surface 20 a where the adhering swarf 9 remains on the outer circumferential portion 20 b. When the workpieces 1 are repeatedly polished on the holding surface 20 a by the polishing unit 26, the swarf 9 is deposited in successively layers on the outer circumferential portion 20 b of the holding surface 20 a. When the amount of swarf 9 adhering to the outer circumferential portion 20 b of the holding surface 20 a thus increases, the swarf 9 is liable to enter between the workpiece 1 and the holding surface 20 a. The swarf 9 that has entered between the workpiece 1 and the holding surface 20 a prevents the chuck table 20 from appropriately holding a workpiece 1 to be polished thereon, and hence the polishing unit 26 is unable to polish the workpiece 1 properly.

One solution to the above problem is to eject water to the deposited swarf 9 to clean the holding surface 20 a of the chuck table 20, for example. However, simply ejecting water has a low cleaning effect and is unable to fully remove the swarf 9. A process of mechanically polishing the holding surface 20 a of the chuck table 20 is another option, only the process tends to drag the swarf 9 along the holding surface 20 a and scratch the holding surface 20 a. The polishing apparatus 2 according to the present embodiment solves the problem by cleaning the chuck table 20 where the swarf 9 adheres to the holding surface 20 a of the chuck table 20 with high-pressure steam. To that end, the polishing apparatus 2 includes, for example, a high-pressure steam ejecting unit 58 disposed in the vicinity of the loading/unloading area 22 where the workpiece 1 is loaded and unloaded, for example.

FIG. 7A schematically illustrates in perspective the chuck table 20 to which high-pressure steam is ejected from the high-pressure steam ejecting unit 58. The high-pressure steam ejecting unit 58 includes, for example, a pipe-shaped member including a hollow shank 58 a extending vertically in the Z-axis directions, a hollow arm 58 b extending horizontally from an upper end of the shank 58 a, and a nozzle 58 c mounted on the distal end of the arm 58 b. The high-pressure steam ejecting unit 58 may be arranged such that the shank 58 a is angularly movable about its central axis to turn the arm 58 b to position the nozzle 58 c at a desired position over the chuck table 20. The shank 58 a has a lower end connected to a high-pressure steam supply source, not illustrated. The high-pressure steam supply source includes a heater, not illustrated, for heating water to a predetermined temperature, for example, so that the high-pressure steam supply source can supply steam at the predetermined temperature. The high-pressure steam ejecting unit 58 ejects steam at a temperature of approximately 105° C. under a pressure of approximately 0.3 MPa to the outer circumferential portion 20 b of the holding surface 20 a of the chuck table 20, for example.

For cleaning the outer circumferential portion 20 b of the holding surface 20 a of the chuck table 20, the chuck table 20 is rotated about its central axis at a speed of approximately 30 rpm, for example. At the same time, the high-pressure steam ejecting unit 58 ejects high-pressure steam 60 to the outer circumferential portion 20 b of the holding surface 20 a fully therealong. When the high-pressure steam 60 is ejected to the outer circumferential portion 20 b of the holding surface 20 a, the high-pressure steam 60 is applied to the swarf 9 adhering to the outer circumferential portion 20 b, softening the swarf 9 because the swarf 9 is heated and exposed to water. As the high-pressure steam ejecting unit 58 continuously ejects the high-pressure steam 60, the swarf 9 is peeled off from the outer circumferential portion 20 b and removed therefrom. While the high-pressure steam ejecting unit 58 is ejecting the high-pressure steam 60, water may be ejected from the porous member that provides the holding surface 20 a of the chuck table 20. The ejected water prevents the swarf 9 peeled off from the outer circumferential portion 20 b from entering the porous member, but discharges the swarf 9 outside of the holding surface 20 a of the chuck table 20. Therefore, the peeled-off swarf 9 is restrained from being deposited again on the holding surface 20 a.

The nozzle 58 c of the high-pressure steam ejecting unit 58 may be oriented downwardly in the vertical directions, i.e., the Z-axis directions. Since steam has a tendency to ascend in the atmosphere, when the high-pressure steam 60 is ejected to the outer circumferential portion 20 b of the holding surface 20 a directly from above, the high-pressure steam 60 acts efficiently on the swarf 9. Alternatively, the nozzle 58 c of the high-pressure steam ejecting unit 58 may be inclined at a predetermined angle to the Z-axis directions so as to face against the direction in which the chuck table 20 rotates at the spot where the high-pressure steam 60 is applied to the outer circumferential portion 20 b of the holding surface 20 a. The nozzle 58 c thus inclined ejects the high-pressure steam 60 in a direction opposite the direction of travel of the swarf 9 on the outer circumferential portion 20 b of the holding surface 20 a as the chuck table 20 rotates, so that the high-pressure steam 60 acts intensively on the swarf 9. According to the present invention, however, the nozzle 58 c of the polishing apparatus 2 is not limited to the downward or inclined orientation.

As described above, the polishing apparatus 2 according to the present embodiment is capable of easily removing the swarf 9 from the outer circumferential portion 20 b of the holding surface 20 a of the chuck table 20 by ejecting the high-pressure steam 60 to the swarf 9 adhering to the outer circumferential portion 20 b. FIG. 7B schematically illustrates in perspective the chuck table 20 from which the swarf 9 has been removed from the outer circumferential portion 20 b of the holding surface 20 a thereof. Since the chuck table 20 whose holding surface 20 a has been cleaned is able to hold a new workpiece 1 under suction thereon without fail, the polishing unit 26 can polish the workpiece 1 properly.

A polishing method according to the present embodiment for polishing a workpiece on the polishing apparatus 2 and cleaning the outer circumferential portion 20 b of the holding surface 20 a of the chuck table 20 will be described below. FIG. 8A is a flowchart of a sequence of steps of an example of the polishing method according to the present embodiment.

In the polishing method according to the present embodiment, holding step S10 is first carried out to place a workpiece 1 on the holding surface 20 a and hold the workpiece 1 on the chuck table 20. FIG. 4 schematically illustrates holding step S10 in perspective. In holding step S10, the X-axis movable table 18 is positioned in the loading/unloading area 22, and the workpiece 1 that has been adjusted in position by the positioning table 12 is loaded onto the holding surface 20 a by the workpiece loading mechanism 14. At this time, the face side 1 a of the workpiece 1 to which the protective tape 3 is affixed is oriented downwardly toward the holding surface 20 a, and the reverse side 1 b of the workpiece 1 as a surface to be polished is oriented upwardly. Then, the suction source connected to the chuck table 20 is actuated to hold the workpiece 1 under suction on the chuck table 20. Thereafter, the X-axis movable table 18 is moved to the processing area 24.

Next, polishing step S20 is carried out to polish the workpiece 1 with the polishing pad 44 b while supplying the slurry to the workpiece 1 held on the chuck table 20. FIG. 5 schematically illustrates polishing step S20 in perspective. In polishing step S20, the chuck table 20 and the polishing wheel 44 are rotated about their respective central axes. Then, while the polishing fluid supply source 48 is supplying the slurry through the polishing fluid supply passage 50 to the reverse side 1 b of the workpiece 1, the polishing unit 26 is lowered to bring the polishing pad 44 b into contact with the reverse side 1 b of the workpiece 1. At this time, the slurry enters between the polishing pad 44 b and the workpiece 1, and the reverse side 1 b of the workpiece 1 is polished to a flat surface. Swarf produced from the workpiece 1, etc., when the workpiece 1 is polished by the polishing pad 44 b is entrained in the slurry and transferred to an outer circumferential edge of the workpiece 1. The slurry, denoted by 56, that has entrained the swarf drops off onto the outer circumferential portion 20 b of the holding surface 20 a of the chuck table 20, and some swarf from the slurry 56 adheres to the outer circumferential portion 20 b.

Next, unloading step S30 is carried out to unload the workpiece 1 polished in polishing step S20 from the chuck table 20. In unloading step S30, the X-axis movable table 18 is moved to the loading/unloading area 22, the workpiece 1 is released from the chuck table 20, as illustrated in FIG. 6, and the workpiece 1 is delivered to the spinner cleaning device 52 by the workpiece unloading mechanism 16. The spinner cleaning device 52 cleans and spin-dries the workpiece 1, which is then stored in the cassette 8 b by the workpiece deliver robot 10.

In the example of the polishing method illustrated in FIG. 8A, after the workpiece 1 has been unloaded from the chuck table 20, swarf removing step S40 is carried out to remove the swarf 9 deposited on the outer circumferential portion 20 b of the holding surface 20 a of the chuck table 20 by ejecting the high-pressure steam 60 from the high-pressure steam ejecting unit 58 to the swarf 9 deposited on the outer circumferential portion 20 b. FIG. 7A schematically illustrates swarf removing step S40 in perspective. In swarf removing step S40, the nozzle 58 c of the high-pressure steam ejecting unit 58 is oriented toward the outer circumferential portion 20 b of the holding surface 20 a of the chuck table 20. Then, the nozzle 58 c ejects the high-pressure steam 60 toward the outer circumferential portion 20 b of the holding surface 20 a. At this time, the chuck table 20 is rotated about its central axis at a predetermined speed. The swarf 9 adhering to the outer circumferential portion 20 b is now softened by being heated and exposed to water, and then removed from the outer circumferential portion 20 b by following part of ejected high-pressure steam 60. In swarf removing step S40, water is ejected from the porous member that provides the holding surface 20 a of the chuck table 20 to prevent the swarf 9 removed from the outer circumferential portion 20 b from entering the porous member. FIG. 7B schematically illustrates in perspective the chuck table 20 that has been cleaned to remove the swarf 9 therefrom. As described above, according to the example of the polishing method illustrated in FIG. 8A, the swarf 9 can be removed easily from the outer circumferential portion 20 b of the holding surface 20 a.

In the polishing apparatus 2 according to the present embodiment, the high-pressure steam ejecting unit 58 for ejecting the high-pressure steam 60 to the holding surface 20 a of the chuck table 20 may be disposed in the vicinity of the processing area 24. In the polishing method according to the present embodiment, swarf removing step S40 may be carried out while polishing step S20 is being carried out. FIG. 8B is a flowchart of a sequence of steps of another example of the polishing method in which swarf removing step S40 is carried out in polishing step S20. The high-pressure steam ejecting unit 58 that is disposed in the vicinity of the processing area 24 is capable of ejecting the high-pressure steam 60 to the outer circumferential portion 20 b of the holding surface 20 a of the chuck table 20 while the polishing unit 26 is polishing the workpiece 1. In this case, the ejected high-pressure steam 60 can remove the swarf from the outer circumferential portion 20 b before the temperature of the slurry containing the swarf that has reached the outer circumferential portion 20 b becomes low enough to dry the swarf and let it adhere to the outer circumferential portion 20 b.

In the present example of the polishing method, the high-pressure steam 60 may possibly enter between the polishing pad 44 b and the reverse side 1 b of the workpiece 1, tending to lower the concentration of the slurry. However, the amount of water supplied in the form of steam from the high-pressure steam ejecting unit 58 to the holding surface 20 a of the chuck table 20 is extremely small compared to the amount of ejected under high pressure to the outer circumferential portion 20 b of the holding surface 20 a. Therefore, any adverse effect that the ejected high-pressure steam 60 has on the polishing process is minimum. Further, inasmuch as a new workpiece can be loaded onto the chuck table 20 after the polished workpiece 1 has been unloaded from the chuck table 20, the example of the polishing method illustrated in FIG. 8B is capable of efficiently polishing a plurality of workpieces 1 in succession.

Further, in the polishing method according to the present embodiment, swarf removing step S40 may be carried out prior to holding step S10. FIG. 8C is a flowchart of a sequence of steps of still another example of the polishing method in which swarf removing step S40 is carried out prior to holding step S10. For polishing a plurality of workpiece 1 one after another on the polishing apparatus 2, when a new workpiece 1 is to be loaded onto the chuck table 20, a problem arises out of swarf 9 deriving from the workpiece 1 previously polished by the polishing unit 26 and adhering to the outer circumferential portion 20 b of the holding surface 20 a. To solve the problem, swarf removing step S40 may be carried out prior to holding step S10 to clean the holding surface 20 a with the high-pressure steam 60 ejected thereto.

Specifically, swarf removing step S40 may be considered to be a step carried out in advance for properly polishing a workpiece 1. Swarf removing step S40 may also be considered to be a step for removing swarf 9 produced from polishing a workpiece 1 in polishing step S20 and adhering to the outer circumferential portion 20 b of the holding surface 20 a. At any rate, the polishing method according to the present embodiment applies the advantages of appropriately holding a workpiece 1 on the chuck table 20 and properly polishing the workpiece 1 to all workpieces to be polished on the polishing apparatus 2. The polishing method reduces the workload required to change and clean the chuck table 20 and the downtime of the polishing unit 26, resulting in an increase in the efficiency with which to process workpieces 1.

The present invention is not limited to the embodiment described above, but many changes and modifications may be made in the embodiment. For example, while the polishing of workpieces 1 on the polishing apparatus 2 for polishing workpieces 1 has been described in the above embodiment, the polishing apparatus 2 may have a grinding unit, not illustrated, for grinding workpieces 1 in addition to the polishing unit 26 for polishing workpieces 1. A workpiece 1 held on the chuck table 20 may be ground by the grinding unit and thereafter may be polished by the polishing unit 26. In this case, in addition to the swarf 9 produced from polishing the workpiece 1, swarf produced from grinding the workpiece 1 is also deposited on the outer circumferential portion 20 b of the holding surface 20 a of the chuck table 20. However, the swarf 9 and the latter swarf can be removed by ejecting the high-pressure steam 60 from the high-pressure steam ejecting unit 58 to the outer circumferential portion 20 b. Accordingly, when a new workpiece 1 is placed on the chuck table 20, the swarf 9 and the latter swarf will not prevent the chuck table 20 from appropriately holding the workpiece 1.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention. 

What is claimed is:
 1. A polishing apparatus for polishing a workpiece, comprising: a chuck table having a holding surface for holding the workpiece placed on the holding surface under suction thereon; a polishing unit for polishing the workpiece held on the chuck table with a polishing pad while supplying a slurry to the workpiece; and a high-pressure steam ejecting unit having a nozzle for ejecting high-pressure steam to the holding surface of the chuck table, wherein the high-pressure steam ejecting unit ejects high-pressure steam to swarf produced from polishing the workpiece and deposited on an outer circumferential portion of the holding surface for thereby removing the swarf from the holding surface.
 2. A polishing method to be carried out by a polishing apparatus including a chuck table for holding a workpiece placed on a holding surface under suction and a polishing unit for polishing the workpiece held on the chuck table with a polishing pad while supplying a slurry to the workpiece, the polishing method comprising: a holding step of placing the workpiece on the holding surface and holding the workpiece on the chuck table; a polishing step of polishing the workpiece held on the chuck table with the polishing pad while supplying the slurry to the workpiece; an unloading step of unloading the workpiece polished in the polishing step from the chuck table; and a swarf removing step of ejecting high-pressure steam to swarf produced from polishing the workpiece and deposited on an outer circumferential portion of the holding surface for thereby removing the swarf from the holding surface. 